AND PROTOPLASTIC POISONS 213 



infectious diseases, and we are left unable to trace with certainty 

 the causation of the disease ta any particular micro-organism. 



A good example of this is to be met with in the case of ordinary 

 vaccine. As is now well known, thanks to the labours of Copeman 

 and of Green, this can be kept in contact with glycerine, or, 

 better, with chloroform water, until all extraneous organisms have 

 perished, and nothing can be grown from the preparation in culture 

 media; yet the virus is still present in almost unabated power, 

 as is shown by obtaining the typical effect on vaccination. 



The virus may here either be a very resistant spore, which 

 remains alive after all the other organisms have been destroyed 

 by the chloroform, which cannot be cultivated upon ordinary 

 nutrient media, and only commences to develop in the serum of 

 the living body after vaccination; or it may be that the virus 

 of vaccine, as suggested by the writer, 1 is an enzyme with the 

 property of reproducing itself in the manner indicated under the 

 heading of autocatalysis. 



The theory of infection held at the present day includes as an 

 axiom that all infection must be carried by micro-organisms or 

 parasites. Now, although this has been incontrovertibly demon- 

 strated in many cases, in just as many others, and these including 

 the most common infectious diseases, in spite of innumerable 

 attempts no causal connection with any definite parasite or micro- 

 organism has been shown to exist. 



If the above-mentioned axiom is granted, then it follows that 

 vaccine prepared with chloroform must contain an undemon- 

 strable living germ, but otherwise the experimental evidence is 

 far more strongly in favour of the virus being an enzyme, reproduc- 

 ing itself in the manner described under Autocatalysis. 



At any rate for the present, the case may serve as an example 

 of how difficult it often is to decide whether a given action is the 

 result of an enzyme or a living cell, because the same agencies 

 which affect one similarly affect the other. 



NEGATIVE CATALYSTS. 



The catalysts which we have hitherto been considering are 

 those which, by their action in diminishing resistance, increase 

 the velocity of a reaction, but a number of substances are known 



1 " A Chemical Theory as to the Propagation and Development of certain 

 Infectious Diseases," The Journal of State Medicine, April, 1904. 



